This invention relates generally to the field of electrical energy production and storage and, more particularly, to an apparatus and method for controlling the charging and discharging of a rechargeable electrical energy storage device, such as a rechargeable battery, by an electrical energy source, such as a solar panel.
A number of techniques have been proposed for controlling the charging and discharging of a storage battery. When the signal from the source is subject to substantial variation, a voltage regulator is often used to lower the voltage of the signal from the source to the approximate voltage of the fully charged device. As the device is charged, the current from the regulator to the device automatically decreases as the device voltage increases, substantially terminating the charging when the voltage of the device is matched with the voltage of the source signal. The foregoing technique has been used to control the charging of rechargeable batteries by solar panels.
Another approach has involved direct charging of a storage battery through a relay, and, at other times, trickle charging through a regulator. The direct connection is terminated when a charge termination level has been reached, and may not be resumed until after the disconnected signal of the source has passed below a chosen level (at night) and subsequently passed above that level (when the sun rises).
Two other related techniques of charge control are disclosed in U.S. patent application Ser. No. 113,936, filed Jan. 21, 1980, having John W. Yerkes and Terry Staler as inventors, and U.S. patent application Ser. No. 222,208, filed Jan. 2, 1981, having Terry Staler as inventor, both of which have been assigned to Atlantic Richfield Company. These applications relate to apparatuses in which a direct connection between a solar panel and a battery is broken at preselected intervals to permit the voltage levels of the solar panel and the battery to be tested. The ratio of the voltages is examined upon disconnection to determine whether reconnection should be made. The technique of Ser. No. 222,208 involves a second float charge mode which is implemented when the solar panel and battery voltages indicate that direct charging should cease. It further incorporates discharging control in a context which requires manual intervention at a significant juncture.
Other techniques known to applicant for controlling the discharging of a battery through a load, in conjunction with charging control, involve disconnection of the load when the battery voltage passes below a discharge prevention threshold, and subsequent reconnection of the load when the battery voltage passes above a higher load reconnection threshold. As far as applicant is aware, such load control apparatuses have operated independently of any control of charging.
Therefore, in many applications, it is desirable to provide an apparatus and method for simply and economically controlling both the charging of a battery by an electrical source and discharging of the battery through a load, while protecting the battery from repeated deep discharge.